pacman -Syu jdk-openjdk

automatically remove

       -u, --upgrades
           Restrict or filter output to packages that are out-of-date on the
           local system. Only package versions are used to find outdated
           packages; replacements are not checked here. This option works best
           if the sync database is refreshed using -Sy.

try pacman -Sy jdk-openjdk

https://bbs.archlinux.org/viewtopic.php?id=290066

Wow I am just now seeing the Arch docs. They are wrong. That’s pretty sad.